feat(puzzles): implement puzzle solution submission and verification …

[Robinsonchiziterem]

PR: Implement Puzzle Solution Submission and Verification API
This pull request implements the core infrastructure for submitting and verifying puzzle solutions, as outlined in GitHub issue #141.

Summary of Changes
🧩 Core Infrastructure
New Entity: Added
PuzzleSolutionAttempt
to track every submission attempt with:
SHA-256 hashed answer storage for security.
Nonce-based anti-replay protection.
Detailed timing, reward, and fraud metadata.
Service Layer: Implemented
SolutionSubmissionService
to orchestrate:
Rate limiting (max 5 submissions / 60s).
Answer verification with normalisation (case-insensitivity, object key ordering).
Server-side timing validation against puzzle time limits.
Fraud detection for "impossibly fast" completions.
Atomic reward and aggregate statistic updates.
🛡️ Anti-Cheat & Security
Integrated with
AntiCheatService
to report suspicious completion times.
Implemented SHA-256 hashing for all answer comparisons.
Added strict nonce uniqueness enforcement to prevent replay attacks.
🚀 API Endpoints
POST /puzzles/:id/submit: Submit a solution for verification.
GET /puzzles/:id/submissions: Retrieve current user's history for a specific puzzle.
GET /puzzles/submissions/history: Retrieve full submission history for the authenticated user.
✅ Verification
Added a comprehensive test suite in
src/puzzles/tests/solution-submission.service.spec.ts
(35+ test cases).
Covered edge cases including:
Correct/incorrect answers.
Answer normalization.
Time limit expiration.
Replay attacks.
Fraudulent timing.
Rate limit exhaustion.
Closes #141

[Mkalbani]

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